The goal of this investigation is to assess the efficacy of a novel anti-angiogenic agent comprised of Shiga-like toxin A fused to vascular endothelial growth factor (SLT-VEGF) alone and in combination with another anti-angiogenic compound, IFN-alpha, in inhibiting the growth of human endothelial precursor cells in vitro and that of human melanoma tumors grown in nude mice. A pharmacological audit trail will be established in the proposed experiments to determine: 1) the presence of the SLT-VEGF target molecule, VEGF receptor-2 (KDR), on human endothelial cell colonies and in the vasculature of human melanoma tumors, 2) the degree of apoptosis induced by SLT-VEGF treatment alone and in combination with IFN-alpha, 3) the pharmacodynamic effects of SLT-VEGF alone and in combination with IFN-alpha on the IC50 of human endothelial precursor cells in vitro and 4) the biologic effects of SLT-VEGF alone and in combination with IFN-alpha on human melanoma tumor growth in vivo and on changes in serum levels of angiogenesis-related compounds. In addition the efficacy of SLT-VEGF alone and in combination with IFN-alpha in preventing metastatic disease will be assayed by treating mice whose primary melanoma tumor explants have been surgically removed. The information obtained in this study will provide a rational basis for deciding whether SLT-VEGF alone or combined with IFN-alpha will be suitable for further development and testing in clinical trials with human patients. [unreadable] [unreadable]